There are known time bases of the aforementioned type wherein there is provided a circuit for adjusting the frequency of the clock signal or the respective frequencies of several clock signals. This adjustment circuit is generally formed by a clocking pulse inhibition circuit in the division chain, the inhibition circuit being arranged to inhibit a certain integer number of clocking pulses at one stage in the division chain in each inhibition period. In general, it is arranged that the clocking pulses are inhibited in the first division stages to obtain improved resolution.
In particular, there are known electronic timepiece movements provided with such a time base, wherein the quartz oscillator produces a periodic signal whose frequency Fosc is slightly higher than a frequency equal to 32.768 Hz (commonly called a 32 Hz signal). The frequency divider circuit is formed by a division-by-two chain. The choice of oscillator frequency is thus understood, since 32.768=215. The inhibition circuit acts, for example, on the second division stage, more precisely at the input of the second stage where the clocking frequency corresponds to the oscillator frequency Fosc divided by two. A reference frequency Fref=32.768/2=16.384 can thus be defined. The integer number Ninh of clocking pulses to be inhibited in each inhibition period Pinh is generally obtained by taking the rounded integer value of the difference between Foscdet/2 and Fref multiplied by the inhibition period Pinh, namely (Foscdet/2−Fref)·Pinh rounded to the unit, where Foscdet is the frequency determined for the periodic signal. This frequency determination is either obtained by an initial measurement, or by a calculation taking account of the measured temperature by using a predefined polynomial which expresses the dependency of the oscillator frequency as a function of temperature. The resolution obtained is thus given by 1/(2·Fref·Pinh). It is therefore understood that, in order to increase the resolution and thus the precision of the time base long term, it is necessary to increase period Pinh. This situation causes a first problem arising from the fact that the maximum instantaneous error increases proportionally with this period Pinh. This problem may be crucial in a time base precision test performed over a relatively short test period, for example of several hours. Further, given that inhibition is generally performed in a short interval of each period Pinh, a second problem arises from the fact that the clock signal or signals is/are disrupted during this short interval. Thus, in each inhibition period, there is a signal with a non-adjusted frequency and, for example, at the end of the inhibition period, the intended integer number of clocking pulses is inhibited, with the clock signal then ceasing to provide a periodic signal during this inhibition.